All about compression

We continue with the very basics of mixing. Following the EQ we are going to consider compression.
There are five key parameters that matter when it comes to compression: ratio, threshold, attack, release and gain.

Learning how to use compressors become much easier once you have an understanding of each of these settings.

Let's take a look at all these parameters in more detail:

Ratio

To understand ratio, we first need to understand what a compressor actually does. When a sound gets too loud, the compressor kicks in and reduces the volume. The ratio determines how much the volume is reduced by.

For example:

You load up a compressor on the vocal and it goes over the threshold by 10dB. We have set the ratio to 2:1. This means that the sound will be reduced in volume by a factor of 2. So, instead of getting 10dB louder, the vocal now gets 5dB louder.

It's important to understand that the signal is compressed only when the audio passes over the threshold.

Threshold

Threshold is the point that the compressor kicks in. If we set the threshold to -24dB, the compressor will not affect everything quieter than that. But, as soon as the sound hits -24dB, the compressor will kick in and reduce the volume.

Here's a graph that ties threshold and ratio all together:
If you set the threshold too low, the audio will be compressed all the time and sound unnatural. We usually use a compressor to catch the louder peaks and make the track more consistent in volume. On the other hand, if we set our threshold too high, the compressor won't do anything at all.

Attack

Attack time is how quickly the compressor engages and reduces the volume of the audio. Different attack times can make a huge difference.

And it all depends on the instrument that you're compressing, the pace of the song, and hundreds of other factors.

We recommend to start with a slow attack time. You should be nearer 40ms to begin with.

This means that the whole note is compressed, rather than the attack of the note (the plectrum hitting the string of a guitar, for example). Because we are talking about milliseconds, everything is happening on a very small scale.

Sometimes you might want a fast attack e.g. a guitarist that picks really hard. Use shorter attack times to when you want to compress the transient as well as the sustain. But in most cases, a slow attack will sound a lot more natural and musical.

With vocals, it works slightly differently. Slow attack sometimes sounds unnatural and odd. Stay around 2-10ms for vocals and voice.

Release

The release time is the exact opposite of attack. This is how long it takes for the compressor to return the audio to its normal volume after the audio drops below the threshold.

If the release time is too quick, the audio will sound very unnatural. But, if it's too slow, the compressor never turns off.

The best way to adjust release time is tweak it until the audio feels right with the rhythm and tempo of the song. There is no exact setting that suits every song or instrument. Start around 60ms and trust your ears.

Here's another chart, this time depicting how attack and release time affect the compression.

The red line is the original audio, and the blue line is the audio coming out of the compressor. Notice how the output lags behind the input due to the attack and release time of the compressor:
Gain

Gain is applied to increase the volume of the audio coming out of the compressor. It can be called "make-up gain", as well as "output gain" control.

A lot of compressors have an 'auto-gain' feature, but you should avoid this. Instead, increase the gain until your level coming out is the same as your level going in (most compressors have dB meters).

Because we are reducing the volume of the loudest peaks, we can increase the overall volume of the track.


Let's take a look at the best, in our opinion, plugin compressors available today:

1. FabFilter Pro-C 2
All the FabFilter plugins always offer something exclusive. They are also surprisingly ergonomic and easy to use. The latest version of your favorite plugin added another 5 compression algorithms (Vocal, Bus, Mastering, Punch and Pumping), as well as 4x oversampling. A great feature of listening to the processed and unprocessed audio in isolation was also moved from FabFilter EQs. A very useful feature, especially for novice producers and sound engineers. That's why we put Pro-C 2 in the first place ranking.

Available in for Mac (32/64-bit, all formats) and PC (32/64-bit, all formats).


2. Waves CLA Classic Compressors
You are sure to find these 4 plugins (CLA-76 "Bluey" and "Blacky", CLA-2A and CLA-3A) in the studios of the best soundmen.

Because each compressor operates differently, you will definitely find a device in this bundle that assists you any time you require compression.

Here's what each one can do for your production:

The CLA-76 is a really quick compressor that works superbly with fast, dynamic input signals such as drums and percussion.

The CLA-2A isn't really used to control dynamics as you would with a regular compressor. This rather slow compressor is widely used mainly because of its character/tone.

The CLA-3A is a compressor/limiter plugin based on a famous solid state unit from the 70's known for its unique transparent compression curve. This compressor works the best with basses and guitars since it adds harmonic distortion to the input signal.

Available in for Mac (32/64- bit, all formats) and PC (32/64- bit, all formats).


3. Cytomic The Glue
A favorite of many producers for its ability to emulate the legendary SSL compressor from the 1980s. Featuring a functional and attractive GUI. If you're looking for that indefinable something extra to bring some analogue life and literally help meld your tracks into cohesive mixes, this is a great place to start. Preferably applied for mix buss and master buss compression.

Available in for Mac (32/64-bit, VST, AU and RTAS) and PC (32/64-bit VST).


Let's summarize.

Compressor is one of the most important tools in mixing. It helps to control the dynamic range of the processed signal. But, keep in mind that you should apply compression only when necessary. Try to catch the problem first, imagine the desired result, plan how to achieve it, and only then add a device to the track.

We hope the above information will positively impact your production. If you already have tracks to be listened to in more than 2,500 establishments of our clients – register on our portal!

Music experts team,
ExpertMusic.

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